Here are some reasons why it's better to use a point-of-sale system to do stock control rather than a manual system.
Manual systems involve a lot of work over a short period of time, frequently extra staff has to be put on. Often the shop needs to be closed to do the stock take. It wastes peoples' time and your money. An automatic system can use location stocktake so the work is done when your staff has some free time.
An automatic system provides real-time stock data. If a customer is in the shop and wants a certain item, your computer systems knows if you have it in stock. If you are doing orders, you need quantities as of now. As you do not get current figures, you can only reconcile to a set period often a financial year.
Because it is easier often a manual system is only reconciled to a dollar figure and not a quantity by stock item.
It is very hard to reconcile a manual system as it is out-of-sync with your actual stock quantites. If it saids you have 10 of an item, you look see you have 9 now has one been sold or one been stolen? You do not know.
Sale trends required for informed forecasts are difficult with a manual stock take system so it is very difficult to determine what is tied up in unnecessary stock. A point of sale system can give you these figures based on any period you require.